Communications using the Internet have been widely used all over the world, and the usage frequency and the amount of information thereof have exponentially increased. Users can transmit and receive desired information by the use of various computer devices such as personal computers and mobile devices. The OSI (Open Systems Interconnection) 7 layers established by the ISO (International Organization for Standardization) is known as a communication standard therefor.
Layer 7: Application Layer
Layer 6: Presentation Layer
Layer 5: Session Layer
Layer 4: Transport Layer
Layer 3: Network Layer
Layer 2: Data Link Layer
Layer 1: Physical Layer
The TCP/IP is actually used on the basis of the OSI 7 layers. The TCP/IP generally includes four layers.
Application Layer: HTTP, FTP, TELNET, SSH, SIP which correspond to Layers 7 to 5 of the OSI
Transport Layer: TCP, UDP, SCTP which correspond to Layer 4 of the OSI
Internet Layer: IP which corresponds to Layer 3 of the OSI
Network Access Layer: MAC which corresponds to Layers 2 and 1 of the OSI
In the WWW, data is transmitted in accordance with a communication protocol called “HTTP (Hyper Text Transfer Protocol)” and information details are displayed on a screen using a file described in the hyper text markup language (HTML) or the like.
When a user calls a service provider, the user gives a call with a general phone. In this case, the user pays the cost or the user calls free with the telephone number in which the service provider pays the cost. When the user gives a call with a VoIP phone using the Internet, the opposite may be a phone connected to the Internet line or a phone connected to a general telephone line.
In the phones which are connected by an Internet service provider (ISP), services for communications of voice, video, and data (for example, “Skype” and “MSN Messenger”) are widely used between VoIP soft phone users. When the user pays the cost, the services may permit a telephone call with a general telephone line. The services are provided to corporate VoIP soft phones (such as Cisco IP SoftPhone) accessing virtual Private Networks (VPNs) for use in companies. In the services provided by the Internet Service Providers, the phones can be connected on line to give a call only when they use the VoIP soft phone service of the same ISP. When even subscribers of the same VoIP soft phone service are not on line, the telephone call is not possible.
The VoIP soft phone users of the ISP connected to the Internet line communicate with each other by the use of the ISP's relay. In this case, the communications are recognized and made on the basis of the IP addresses corresponding to Layer 3 which is the network layer among the OSI 7 layers and the SIP (Session Initiation Protocol) information corresponding to Layer 5 which is the session layer. However, specifications other than the SIP may be used depending on the situations.
When a VoIP soft phone user gives a call to an opposite connected to a general telephone line, a communication based on the IP addresses is established between the VoIP soft phone user as a client and the ISP, and a communication using an existing telephone network is established between the ISP and the general phone.
On the other hand, as the primary related art, the VoIP-based SIP session protocol corresponding to Layer 5 which is the session layer among the OSI 7 layers is defined by the IETF (Internet Engineering Task Force) and becomes an international standard.
Most users want to give a call to an external phone of a service provider or an affiliate of the service provider, when the user's phone gives a call to the phone of the service provider or the affiliate with his or her charge, when the user's phone gives a call to a telephone number for which the service provider or the affiliate pays the cost, and when the user's VoIP soft phone gives a call to the general phone of the service provider or the affiliate.